Which Angles Match
Part of the Angles section of Coddy's Geometry journey. Lesson 49 of 62.
The ticks decide which pair matches, and reading them wrongly is this chapter’s classic error. The equal angles sit opposite the ticked sides, never simply “at the bottom”: rotate the triangle and the base pair rotates with the ticks.
In the figure the ticked sides run from the apex down, so the matching angles are the two at the ends of the unticked base: 40° and 40°, opposite the ticks. The apex, held by both ticked sides, matches nobody, and here it is the wide 100° corner. Ticks first, conclusions second.
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Angles
1Meet the Angle
Your First AngleNaming AnglesAdding Adjacent AnglesDegrees and the Full TurnAcute, Right, ObtuseRecap: Adjacent Angles4Vertical Angles
Linear PairsVertical Angles Are EqualSolving with VerticalsAll Four AnglesRecap: At the Crossing7Crossing Parallel Lines
Parallel LinesCorresponding AnglesAlternate AnglesCo-interior AnglesWhich Rule Is ItRecap: The Three Pairs10Isosceles Triangles
Base Angles Are EqualFinding the ApexWhich Angles MatchEquilateral AnglesIsosceles at WorkRecap: Twin Corners2Straight Lines and Supplements
Angles on a LineSupplementary AnglesThree Angles on a LineWrite the EquationRecap: Along the Line5Around a Point
Angles Around a PointThe Missing AngleEqual SlicesFour Angles, One PointRecap: The Full Turn3Right Angles and Complements
Complementary AnglesFinding the ComplementPerpendicular LinesEqual Parts of a CornerRecap: The Right Corner6The Angle Bisector
The Angle BisectorBisected ExpressionsBisecting a Straight AngleRecap: Split in Half